BIOLOGICAL DATA AND HABITAT REQUIREMENTS

WILDLIFE SPECIES: Anas strepera
TIMING OF MAJOR LIFE HISTORY EVENTS :
Breeding and nesting - The gadwall's breeding season varies but usually
occurs in May through mid-July, somewhat later in the northern regions
and earlier in the south [2,11].
Clutch/incubation - Gadwalls lay 5 to 13 eggs per nest, and incubation
is 24 to 28 days [1,13].
Fledge - Gadwalls fledge 7 to 8 weeks after hatching [6].
Maturity - Gadwalls become sexually mature and acquire their breeding
plummage during their first winter [6].
Migration - Gadwalls are one of the last ducks to arrive on breeding
areas in the spring [1]. Some early dates of arrival for various areas
in North America are as follows [2]:
Southern Iowa - March 10
Minnesota, Heron Lake - March 17
Montana - April 1
Manitoba - April 23
Saskatchewan - April 18
Alberta - May 5
PREFERRED HABITAT :
Gadwall pairs use wetlands for feeding, loafing, and courtship prior to
nesting [16]. They prefer prairie marshes, sloughs, ponds, or small
lakes in grasslands of both freshwater and brackish habitats. They
generally avoid wetlands bordered by woodlands or thick brush,
preferring those bordered by dense, low herbaceous vegetation, or with
grassy islands [6,17,19]. Shallow semipermanent prairie marshes are
preferred over deeper marshes, lakes or temporary water areas [6,16].
Sixy one percent of 1,073 gadwall broods observed over a 20-year period
in North and South Dakota were in semipermanent wetlands [16].
Winter habitat - Gadwalls prefer to winter in freshwater, marshy
habitats and slightly brackish estuarine bays [6,19].
Nesting - Gadwalls nest on well-drained sites on islands in lakes,
upland meadows or pastures, alfalfa fields, or on prairies usually
within 150 feet (45 m) of water. They prefer to nest in uplands rather
than over water [19] and generally select the tallest, densest,
herbaceous or shrubby vegetation available to nest in [16].
COVER REQUIREMENTS :
For escape cover, gadwalls prefer large areas of open water water rather
than with emergents [16]. Tall, dense vegetation provides good nesting
cover for gadwalls. As the vegetative cover increases, the potential
for nest establishment and success increases. Height and density of
vegetation is assumed to be more important than species composition. In
a California study, most gadwall nests were in vegetation 13 to 36
inches (33-91 cm) tall that provided concealment on all sides and above.
No nests were found in herbaceous cover less than 6 inches (15 cm) tall.
Fifty-one percent of nests in North Dakota nesting fields were in
herbaceous cover from 12 to 24 inches (30-60 cm) tall, while 47 percent
were in cover less than 6 inches (15 cm) tall [16].
FOOD HABITS :
Gadwalls are almost exclusively surface feeders. They tend to feed in
rather shallow marshes having abundant aquatic plant life growing close
to the surface [6]. They sometimes feed in stubble fields for grain or
in woods for acorns [19]. They mainly consume leaves and stems of
aquatic plants but also eat insects, mollusks, crustaceans, amphibians,
and fishes [9,16,19]. Aquatic plants commonly eaten by gadwalls include
pondweed (Potamogeton spp.), widgeongrass (Ruppia maritima), saltgrass
(Distichlis spp.), muskgrass (Chara spp.), eelgrass (Zostera marina),
spikerush (Eleocharis spp.), spiked watermilfoil (Myriophyllum spicatum)
and filamentous algae [9,16,19]. The two most prominent plants in the
diet of gadwall in South Carolina are fragrant flatsedge (Cyperus
odoratus) and Carolina redroot (Lachnanthes caroliniana). Major animal
foods include crustaceans, especially those belonging to the order
Anostraca, and insects, especially adult and larval chironomids
(Chironamidae) [16].
Recently hatched gadwalls in Alberta initially fed on invertebrates but
were essentially herbiverous by 3 weeks of age. Major animal foods of
ducklings included adult and larval chironamids, water boatman
(Cerixidae), beetles (Coleoptera), and cladocerans (Cladocera).
Important plants in the duckling's diets were pondweed, green algae
(Cladophoracea), duckweed (Lemna minor), and seeds of American
sloughgrass (Beckmannia syzigachne) [16].
PREDATORS :
Predators of gadwalls include humans, foxes (Vulpes spp.), raccoons
(Procyon lotor), striped skunks (Mephitis mephitis), coyotes (Canis
latrans), badgers (Taxidea taxus), weasels (Mustela spp.), minks
(Mustela vison), crows (Corvus spp.), and magpies (Pica spp.)
[8,9,12,14].
MANAGEMENT CONSIDERATIONS :
Grazing and mowing often destroy preferred nesting cover for gadwalls.
Although annual mowing or grazing is not recommended, mowing may be
useful for maintaining vegetative cover in earlier, more productive
successsional stages [16].
REFERENCES :
NO-ENTRY

FIRE EFFECTS AND USE

WILDLIFE SPECIES: Anas strepera
DIRECT FIRE EFFECTS ON ANIMALS :
Late spring and summer fires may destroy gadwall nests [20]. Ducklings
and molting adults are especially vulnerable to fire. When not molting
adult gadwalls can probably easily escape fire.
HABITAT RELATED FIRE EFFECTS :
Burning can change the growth form and pattern of nesting cover for
gadwalls [20]. Gadwalls prefer nesting in dense cover [16], which can
be destroyed by fire. A study of the effects of nesting cover removal
on breeding puddle ducks at Lower Souris National Wildlife Refuge, North
Dakota, showed that after spring burning, nest densities of gadwalls
were greater in areas where the vegetation was not burned [12].
Additionally, gadwall nests were significantly (P<0.01) less abundant in
mowed meadows that would be expected by chance. They made up 29 percent
of all nests found, but only 13 percent of the nests were in mowed
meadows. Gadwalls will, however, use areas that have been burned if
cover development is sufficent when they begin nesting [12]. Changes in
vegetation cover induced by fire can also benefit gadwalls by destroying
unwanted vegetation and increasing vegetation preffed by gadwalls [15].
FIRE USE :
Wetlands can be burned to reverse plant succession to a subclimax plant
community which is attractive to waterfowl [15]. Fire can be used to
remove the accumulation of dead vegetation built up on marshes over the
years and restore wetlands that are dominated with plants such as common
reed (Phragmites communis). Desirable gadwall foods such as pondweed can
be restored by burning. Burning should be postponed until after the
nesting season to avoid destroying nests [15].
FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find Fire Regimes".
REFERENCES :
NO-ENTRY